Dipole Antenna Length Calculator
Calculate the optimal length for a half-wave dipole antenna.
Enter frequency to get total length and each leg length in feet and meters.
A half-wave dipole is the most fundamental antenna in amateur radio. It consists of two equal-length conductors fed at the center, each one-quarter wavelength long (half-wave total).
Formula: Total length (ft) = 468 / frequency (MHz)
The constant 468 comes from the speed of light adjusted for a velocity factor of approximately 0.95 (wire antennas are slightly shorter than a free-space half-wavelength due to capacitive end effects). In free space it would be 492 ft/MHz.
Each leg = 234 / frequency (MHz)
Common amateur radio band dipole lengths:
- 160 m (1.9 MHz): ~246 ft (75 m)
- 80 m (3.65 MHz): ~128 ft (39 m)
- 40 m (7.15 MHz): ~65 ft (20 m)
- 20 m (14.15 MHz): ~33 ft (10 m)
- 10 m (28.5 MHz): ~16.4 ft (5 m)
- 2 m (146 MHz): ~3.2 ft (0.97 m)
Practical notes: Wire dipoles work best installed at least half a wavelength above ground. The feedpoint impedance is approximately 73 ohms, well-matched to 75-ohm coax. Use a 1:1 balun at the feedpoint to prevent feedline radiation. Height above ground significantly affects the actual resonant frequency — you will need to trim the antenna after installation and test with an SWR meter or antenna analyzer.